Certain heretofore known types of disc brake assemblies comprise a pair of pivoted brake-shoe-carrying levers or tongs that are actuated by movement of a wedge member between rollers mounted on the outer ends of the levers to thereby rock these levers until the brake shoes are forced into friction engagement with the opposite sides of a rotor. These heretofore known disc brake assemblies, such as that shown and described in U.S. Pat. No. 3,148,749, issued Sept. 15, 1964, to Eldon W. Bushnell, and assigned to Amsted Industries Incorporated, of Chicago, Illinois, have included a pawl and ratchet type of slack adjuster mechanism to compensate for wear of the brake shoes and/or the rotor. A pawl and ratchet type of slack adjuster mechanism is operative to take up slack, or compensate for wear, in steps or increments, the size of which corresponds to the arcuate distance between two adjacent teeth on a ratchet wheel. Therefore, it is apparent that until a chosen amount of wear has occurred, no compensation therefor is made. Under certain conditions, it is most desirable that wear compensation occur substantially simultaneously as the wear. Thus, in a spring-applied power released brake, the braking force applied to the braking member is reduced as wear occurs. Therefore, it is desirable that wear compensation occur while the brake application is in effect or upon the subsequent brake release.
Accordingly, it is the general purpose of this invention to provide a combined spring-applied fluid-pressure released and fluid power applied disc brake assembly with an automatically operative slack adjuster mechanism that includes spring-biased means that is effective, upon releasing each brake application, to compensate for the wear of the brake shoes and/or the rotor occurring while the brake application was in effect, this means also being effective, while the brakes are released, to constantly lightly press the brake shoes against the rotor thereby maintaining zero clearance therebetween.